How to get selected value in dropdown list, then pass it to views.py

I’m working on an upload file feature with dropdown and dropzone. But, whenever I submit the uploaded file with selected option, it always says that the selected option is None. I found it None after I printed the nama_bimbingan in views.py. Here it is my code.

url.py

....
url(r'bimbingan/add/upload', mengelola_bimbingan.upload_data_bimbingan, name='add-bimbingan-excel'),
url(r'bimbingan/download-template/', mengelola_bimbingan.bimbingan_template, name='bimbingan-template'),
....

forms.py

class UploadBimbinganForm(forms.Form):
    ...
    ...
    dropdown_choices = tuple(zip(all_pembimbing, all_pembimbing))
    nama_pembimbing = forms.ChoiceField(choices = dropdown_choices)

upload_bimbingan.html

<form method="POST" action="{% url 'app:add-bimbingan-excel' %}" enctype="multipart/form-data">
    {% csrf_token %}
    <div class="py-3">
        <label for="id_nama_pembimbing"> Nama Pembimbing Akademik: </label>
        <select class="form-control mb-2" id="id_nama_pembimbing" name="nama_pembimbing" required>
            <option value = "" selected="selected">---------</option>
            <option value = {{form.nama_pembimbing}}></option>
        </select>
    </div>

    <div id="myDropzone" class="dropzone" drop-zone>
        <h6 class="dz-message"> Drop file here or click to upload</h6>
    </div>
            
    <div class="py-3">
        <a href="{% url 'app:bimbingan-template' %}">Download Template</a><br>
        <div class="row justify-content-between py-3">
            <div class="col-md-5 mb-1">
                <a href="{% url 'app:read-all-bimbingan' %}" class="btn btn-blue-outlined">Batal</a
            </div>
            <div class="col-md-5">
                <input type="submit" value="Simpan" class="btn btn-block btn-blue">
            </div>
        </div>
    </div>
</form>

views.py

@login_required(redirect_field_name='index')
@user_passes_test(only_admin_access)
def upload_data_bimbingan(request):
    form = UploadBimbinganForm(request.POST or None)
    if request.method == "POST" and 'file' in request.FILES:
        nama_pembimbing = request.POST.get('nama_pembimbing') 
        excel_file = request.FILES["file"]
        data = get_data(excel_file, column_limit=1)
        bimbingans = data["Bimbingan"]
        ...
        ...  
        if(len(duplicate) == 0):
            space_parsed_query = nama_pembimbing.replace(' ', '%20')
            cleaned_query = space_parsed_query.replace(',', '%2C')
            nip_pembimbing = int(get_data_dosen_by_nama(cleaned_query)[0]["nomor"])
            
            for bimbingan in bimbingans:
                if(bimbingan[0] != "NPM"):
                    new_bimbingan = Bimbingan(nip_pembimbing=nip_pembimbing, npm_mahasiswa=bimbingan[0])
                    new_bimbingan.save()
            return redirect('/app/bimbingan')
        else:
            ...
            ...
            return redirect('/app/bimbingan')
    else:
        context={
            "form": form
        }
        return render(request, 'app/mengelola_bimbingan/upload_bimbingan.html', context)

I already tried to use nama_pembimbing = form.cleaned_data["nama_pembimbing"] in views.py, but it’s still not working since the form.is_valid() always return false, so I removed it. I use django & python for this and purpusely don’t use javascript to handle the uploaded file & selected option. I really hope that someone can help me to resolve this issue.